The present invention relates to manufacturing of metal bellows, and, more particularly, to an apparatus and method for welding metal bellows.
Precision metal bellows are widely used in a number of applications where movement is required, but where sealing is also desired. For example, a bellows may seal a vacuum tightly while acting as a mechanical actuator.
A bellows may be formed by joining together a series of bellows diaphragms in a predetermined pattern. A typical diaphragm is a generally circular disk with concentric folds formed therein. The diaphragms are joined together so that alternate adjacent inside edges are connected together and alternate adjacent outside edges are connected.
The conventional approach to joining metal diaphragms has been to tungsten inert gas (TIG) weld both the inside and outside joints. A weld clamp is used to clamp the inside edges of the diaphragms for welding, and a chill ring or a spacer is used to press the outside edges of the diaphragms together for joining. Unfortunately, the TIG welding is relatively slow and may produce inconsistent quality welds. Conventional welding is described in more detail in U.S. Pat. No. 6,078,021, which patent also describes an improved apparatus and method for bellows welding by applying a laser and a seam tracking technologies.
Even though the apparatus and method of the ""021 patent have improved the bellows welding greatly, there still exists areas of improvements needed to make the bellows welding process more economical. The laser welding that is described in U.S. Pat. No. 6,078,021 improved productivity substantially, but still requires precision copper chill rings or spacers for the outside welding. These spacers are needed to press the diaphragms together for effective welding. For the inside welding, different weld clamps are needed for different sizes of the diaphragms.
U.S. Pat. No. 3,918,622 to Larsen discloses tungsten inert gas welding of the outer joint of a plurality of stacked diaphragms in a rotatable arbor. Since the arbor is made to hold a certain size of diaphragms, many different sizes of arbors are needed to weld variety of diaphragms. Unfortunately, this process has the same problem of high investment in welding fixtures as in the case of conventional welding processes.
Also relating to joining diaphragms to form a metal bellows, U.S. Pat. No. 3,626,582 to Melill discloses diffusion bonding of stacked diaphragms. The fabrication requires pressuring fixture tooling including an external steel cylindrical retainer ring and an internal steel cylindrical retainer plug, together with a force transmitting annular ram and multiple thin steel pressure support rings using to transmit the bonding force of the high pressure ram. The process, unfortunately, is relatively complicated and expensive as it requires elevated temperature operation. Beside, many different sizes of fixtures are needed to braze different size diaphragms.
Stoll in U.S. Pat. No. 4,760,236 discloses a tubular rotating fixture for welding outer and inner seams of annular elements. Unfortunately, the holding fixture is not readily adaptable for different sizes of annular element (diaphragm), and many different sizes of the holding fixtures are needed to weld different size of bellows.
Rancourt discloses an apparatus for welding multiple joints simultaneously in U.S. Pat. No. 5,410,123. An electron beam or laser beam is impinged on a multiple and separate joints to weld. The idea lacks the practicality since majority of the welding power is lost through the spaces between the joints, and only a fraction of the power will be used to weld. Moreover, the power density in this arrangement will not be high enough to initiate welding.
Landtwing, U.S. Pat. No. 5,053,601, discloses a process of stamping and welding in the same stamping press. Even though the idea appears to be economical since you do not move parts around, uncleaned stamped parts will produce defects in welding. This process is not suited for precision welding of thin gage diaphragms for bellows.
Among the several features and advantages of the present invention may be noted the provision of an apparatus and related methods for forming a precision weld at the interior and exterior joints of a metal bellows without the use of expensive chill rings or spacers; minimization of tooling costs of different weld clamps and arbors that are needed in conventional welding of bellows; and the provision of a universal welding fixture for welding different sizes of diaphragms to reduce the manufacturing costs of making a metal bellows.
These and other objects, advantages and features of the present invention are provided by an apparatus for welding the inner and outer joints of a bellows. The apparatus preferably includes three guide wheels for holding and aligning diaphragms to be welded. The guide wheels have V-grooves on their rims to capture and hold the two edges of the adjacent diaphragms for welding. The three guide wheels may be placed at the outside periphery of the diaphragm for outside diameter welding, and may be placed inside the diaphragm opening for inside diameter welding.
One of the wheels is preferably an idler wheel and is attached to a spring-loaded rotary solenoid that may be swung away form the diaphragms for loading and unloading of diaphragms, convolutions and bellows. The idler wheel, when in contact with the diaphragms, pushes the diaphragms against the other two guide wheels for holding and aligning the diaphragm edges. The rotary solenoid may be secured at a different position with respect to the other two guide wheels to accommodate different diameter diaphragms. One or both of the guide wheels may be driven by an electric motor with a gear reduction box to rotate the wheels at a relatively slow speed. The speed and the direction of the electric motor rotation may be controlled by a microprocessor in a personal computer for proper welding.
The heat source for the welding may be an electric arc such as typical tungsten inert gas (TIG), or a laser as described in U.S. Pat. No. 6,078,021. Other types of heat sources including conventional welding sources as well as more esoteric sources, such as an electron beam or plasma, may be used with this apparatus for welding of bellows without departing from the invention. The term xe2x80x9cheat sourcexe2x80x9d thus refers to any suitable welding apparatus for applying concentrated heat to the metal bellows at sufficient intensity to effect melding and welding thereof.